With continuous improvement of people's quality of life, air humidity control device (hereinafter referred to as “humidifier”) is popular with consumers for its function of humidifying dry air, compensating for moisture in the air, improving living comfort and moisturizing the skin. In a dry season, the humidifier has become a common household appliance in modern life, especially the regular use of air-conditioned rooms and dry areas such as the Northwest. An existing humidifier usually has an extractable independent water tank, and a smart valve is installed on the bottom of the water tank. When in use, it is necessary to lift up the water tank and rotate it by 180 degrees, in order to inject water, turn on the control valve, inject water from the control valve port, turn off the control valve, and place the humidifier back to the base, in order for normal use. This is inconvenient operation procedures, because the water tank can be very heavy after having water added. It is inconvenient for infirm persons such as the elderly and the women to use. Meanwhile, because the diameter of the control valve port is limited, it is difficult for the hand to be inserted in water tank, and the cleaning of the internal space of the water tank is inconvenient. To solve this problem, technicians have invented a humidifier that allows water to be added therein from the top of the tank. For example, the electric control devices, such as an electromagnetic valve, a water pump, and a motor are disposed on the humidifier base. However, these devices are expensive and have complicated circuit, resulting in high cost of the humidifier.